FFMI Calculator
FFMI (fat-free mass index) is like BMI, but it counts only your lean mass: muscle, bone, organs and water. Two people with the same BMI can have very different FFMIs, which is why lifters use it to track muscle. Enter your height, weight and body fat, or estimate body fat with a tape measure.
FFMI calculator (fat-free mass index)
Shows how much lean mass you carry for your height. Free, nothing saved.
How FFMI is calculated
- Lean mass = weight × (1 − body fat %)
- FFMI = lean mass in kg ÷ (height in m)²
- Normalized FFMI = FFMI + 6.3 × (1.80 − height in m)
The last step adjusts everyone to the height of a 1.80 m (5 ft 11 in) man, because taller people tend to score slightly lower. Harrison Pope’s group at Harvard (Kouri and colleagues, 1995) introduced it. Many online calculators use 6.1 in this step, but the published abstract gives 6.3. The difference is a tenth of a point or less for most heights.
Worked example: 180 lb is 81.6 kg. At 15% body fat, lean mass is 69.4 kg. At 1.778 m tall, FFMI is 69.4 ÷ 3.161 = 22.0, and the height adjustment adds 0.1, giving 22.1.
What is a normal FFMI?
In a Swiss study of 5,635 healthy adults (Schutz 2002), the median FFMI for people aged 18 to 34 was 18.9 for men and 15.4 for women. Men’s values stayed about the same with age, while women’s rose slightly.
At the high end, Kouri’s 1995 study of 157 male athletes found that men who had never used anabolic steroids reached a normalized FFMI of about 25 at most. Many steroid users were above 25. That doesn’t make 25 a hard rule for any one person, and a low body fat reading that is wrong by a few points can push the result over it.
If you don’t know your body fat
Choose “Estimate it with a tape” and enter your waist and neck (and hips for women). The calculator uses the US Navy circumference equations from Hodgdon and Beckett (1984). They are quick but can be off by several percentage points, so treat the FFMI as a rough figure. A DXA scan gives a more accurate body fat number.
Our lean body mass calculator works without a body fat number, and the body fat calculator explains the tape method in more detail.
Frequently asked questions
What is a good FFMI?
For young adults the median is about 18.9 for men and 15.4 for women (Schutz 2002). A man who lifts regularly might sit around 20 to 23. Values close to 25 are near the top of what drug-free men reached in the Kouri 1995 study.
Is FFMI better than BMI?
For muscular people, yes. BMI counts muscle and fat the same, so a strong person can look overweight. FFMI counts only lean mass, but it needs a body fat estimate, which adds its own error.
Can you get an FFMI over 25 naturally?
Kouri 1995 found drug-free men topped out at about 25, while many steroid users were higher. A few people may exceed it, and errors in body fat measurement can also push the number above 25.
Why is my FFMI normalized for height?
Taller people tend to have slightly lower FFMI at the same build, so the formula adjusts everyone to a 1.80 m man. This makes results comparable between short and tall people.
What FFMI is normal for women?
The median for women aged 18 to 34 in the Schutz 2002 study was 15.4. The 25 ceiling from Kouri 1995 was measured in men and does not apply to women.
Related tools
Sources
- Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med. 1995;5(4):223–228. doi:10.1097/00042752-199510000-00003
- Schutz Y, Kyle UUG, Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18–98 y. Int J Obes. 2002;26:953–960. doi:10.1038/sj.ijo.0802037
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, 1984.
Last updated: 7 November 2026. This tool gives an estimate for general information.